As is well known in the art, brass has been widely used for plumbing fittings and fixtures, and a host of other applications in which it comes into contact with substances intended for human consumption. Brass has found particular applicability for use in the manufacture of faucets, valves, fittings and related plumbing products designed for use in delivering potable water in commercial and residential structures.
Brass is an alloy composed principally of copper and zinc. In virtually all applications, however, relatively small amounts of lead are typically added to the alloy to facilitate metal working of the brass including promoting its machineability. Indeed, machineability is particularly desirable when the brass is to be used for plumbing components since those components generally require the cutting of threads and the like.
The lead atoms, because of their atomic size, are larger than atoms of copper or zinc. As a result, lead exhibits a relatively low solubility in solid solution in brass alloys. Those characteristics of lead thus promotes the tendency of lead to precipitate in lead-rich regions dispersed throughout the brass alloy, and particularly near the surface of the brass. The presence of lead-rich regions near the surface of the brass components provides a real advantage in terms of the machineability of the brass adjacent to the surfaces thereof. Unfortunately, however, that same effect increases the tendency of the lead present on or near the surface to leach into water when the brass is used in plumbing applications.
For many years, the quantity of lead leached into foods and liquids from lead-containing plumbing components was generally regarded as sufficiently low that it presented no substantial risk to humans ingesting foods and liquids that had come in contact with those plumbing components. Recent standards at both the state and federal levels, however, have significantly limited the amount of permissible leaching of lead and lead exposure. One example of the more demanding standards is the Safe Drinking Water Act, amended in 1988 to limit lead in solders and fluxes to 0.2% and to limit lead in public water supply pipes and fittings to 8%. As an additional example, California has promulgated regulations limiting lead exposure of humans to less than 0.5 micrograms per day. The EPA in 1991 restructured the standard of lead in drinking water from 50 parts per billion to 15 parts per billion. More recently, a national standard of 11 parts per billion for lead leaching from plumbing fittings and fixtures intended for use with potable water has been implemented under the 1996 amendments to the Safe Drinking Water Act.
While the amount of lead that can be leached from brass plumbing components is generally low, it has been found that the amount of lead that can be leached from plumbing components may exceed either current or future planned standards. It has also been proposed that such standards be made more stringent, resulting in requirements that either lead be omitted totally from the brass alloy or that the brass be treated to ensure only minimum quantities of lead can be leached from brass components.
Similar limitations have been applied to plumbing components in metering devices to meter water to consumers. Water meters, for example, have typically employed brass components in contact with the water to be delivered for the purpose of preventing or minimizing corrosion of the components of the water meters. The corrosion problem is particularly severe when, as is increasingly the situation, such metering devices are buried within the soil and are therefore exposed to the corrosive effects of minerals in the soil.
In U.S. Pat. No. 5,958,257, filed Jan. 7, 1997, it has been proposed that the leachable lead present in brass components, and particularly brass components employed in plumbing applications, can be reduced by a method of treatment of the brass components. In the method described in that co-pending application, new brass components are initially treated with a caustic solution at an elevated pH for the purpose of removing at least some of the leachable lead in the brass component. After rinsing to remove excess caustic, the brass component is thereafter contacted with a water soluble carboxylic acid to remove the remaining leachable lead. While the method disclosed in that co-pending application represents an advance in the art as compared to prior methods, it is nonetheless subject to limitations. One of the principal limitations of the use of an alkali caustic solution is that the rate of removal of lead is relatively slow. In addition, copper oxide also found on the surface of such brass components should likewise be removed, and caustic is not particularly effective in removing such copper oxides in that respect. The limited ability of caustic to effect removal of copper oxide likewise impacts on the removal of lead. Copper oxide needs to be removed to expose additional quantities of lead at the surface of the alloy, and thus the limitations of caustic in the copper oxide removal likewise inhibit the removal of lead as well.
In addition to those shortcomings, the method disclosed in the foregoing co-pending application suffers from the further limitation that the process, while effective, makes use of reagent solutions whose useful bath life is limited. That, in turn, adds to the cost and reduces the feasibility of operating the process in that caustic must be frequently replaced to maintain lead removal at the required high levels.
It is accordingly an object of the present invention to provide a simple, inexpensive and effective process for the treatment of brass components, and particularly brass components for use in plumbing applications, to reduce the leachable lead therefrom.
It is a more specific object of the invention to provide a method for the treatment of brass components which consistently removes leachable lead to levels far below either present or anticipated federal and state health standards.
It is yet another object of the invention to provide a method for the treatment of brass components to remove leachable lead therefrom which is effective both in the treatment of red brass along with yellow brass.